#include <stdio.h>
//練習問題G
 
int func(int n){
    int a, b=2, c=1;
    int i;
for(i=2;i<n;i++){
	a=2*c-2*b;
	c=b;
	b=a;
}return a;
 
}
int main(void) {
	int n = 3;
    printf("数列anについて, n=%dのときの値は%d\n", n
, func
(n
)); 	return 0;
}
 
				I2luY2x1ZGUgPHN0ZGlvLmg+Ci8v57e057+S5ZWP6aGMRwoKaW50IGZ1bmMoaW50IG4pewogICAgaW50IGEsIGI9MiwgYz0xOwogICAgaW50IGk7CmZvcihpPTI7aTxuO2krKyl7CglhPTIqYy0yKmI7CgljPWI7CgliPWE7Cn1yZXR1cm4gYTsKCn0KaW50IG1haW4odm9pZCkgewoJaW50IG4gPSAzOwogICAgcHJpbnRmKCLmlbDliJdhbuOBq+OBpOOBhOOBpiwgbj0lZOOBruOBqOOBjeOBruWApOOBryVkXG4iLCBuLCBmdW5jKG4pKTsKCXJldHVybiAwOwp9Cg==